A field of application of the invention is automobile security, especially for generating gas serving to inflate an inflatable airbag for protection of a person in a vehicle in the event of shock.
The pyrotechnic charge located in the chamber is ignited by an ignition device to generate gas. Combustion of this pyrotechnic charge releases gas which escapes via a through-hole to the outside of the chamber.
The through-hole is initially closed by a lid sealing the chamber relative to the exterior. The rise in pressure of combustion gases inside the chamber breaks the lid to admit combustion gas of the pyrotechnic charge into the through-hole to the outside of the chamber.
Different types of devices for sealing the chamber are known.
This sealing is necessary so that the pyrotechnic charge contained in the chamber retains its properties of combustion and to prevent it becoming contaminated by external particles or humidity or preventing particles of the pyrotechnic charge from escaping to the outside of the chamber.
A first type of sealing device consists of sticking a sheet against the inner surface of the chamber over the through-hole.
This technique is however difficult to implement due to the fact that the outer wall delimiting the chamber is usually tubular and larger in size than its transversal walls, which makes the chamber oblong and narrow and leaves little place for carrying out adhesion. This technique can cause a substantial rebut rate or considerable costs.
A second type of sealing device consists of doubling with a metallic sheet in the form of a box (“lid box”) the tubular wall and the transversal inner wall delimiting the chamber to reclose the box against a seal gasket borne by the other lateral wall bearing the igniter. But, in the case of a generator whereof the length is much greater than the diameter, it is difficult to manufacture boxes with a constant and controlled thickness of material. In fact, the sheet serves as cap against the through-hole and is a critical component whose thickness defines the uncapping pressure and the uncapping time of the hole after ignition.
Consequently, the result is a thickness of sheet which is predefined and weak enough for the sheet to be able to yield to a gas pressure which is not too high.
In a general manner, it is difficult to make a very long box from a sheet of slight thickness (with a thickness controlled laterally).